Door closer



H. A. GUYER Aug. 23, 1960 DOOR CLOSER 5 Sheets-Sheet 1 Filed Feb. 2l,1956 ATTORNEYS i fi if a H. A. G'UYER Aug. 23, 1960 DOOR CLOSER 5Sheets-Sheet 2 Filed Feb. 2l, 1956 INVENTOR /zfzZe/'Z 'zzzye ATTORNEY H.A. GUYER DOOR CLOSER 5 Sheets-Sheet 4 Filed Feb. 21, 1956 BY/wATTORNEYSl Aug. v23, 1960 HL A. GUYER 2,949,625

. DooR CLOSER Filed Feb. 21, 1956 5 sheets-sheet 5 f6 4W INVENTOR BYLMQMATTORNEYS DOOR CLOSER Hubert A. Guyer, 9 Brookside Drive, RichardsonPark, Wilmington, Del.

Filed Feb. 21, 1956, Ser. No. 566,901` '11 Claims. (Cl. 1652) Thepresent invention relates generally to the field of hydraulics and ismore particularly directed to certain new and useful improvements inautomatic door closers of .the hydro-mechanical type.

Although automatic door closers ofV various types have been well knownin the art for many years, in general their use has tended to be limitedto various commercial applications where the elements ofl initial costand maintenance could be better justified than in the case of domesticor residential dwellings. However, in recent years there has developed adefinite trendtoward the widespread installation of storm. doors inresidential dwellings and, in parallel with this trend, there has alsodeveloped a definite need for an automatic door closer properlyk suitedto the requirements of such installations.

As is well known to those skilled in the art, the use of automatic doorclosers of the hydraulic or hydro-mechanical type has, in the past,involved a number of other difficulties in addition to the relativelyhigh initial cost and maintenance expense as a result of which hydraulicdevices of this type have found restricted. applicability even incommercial installations. One of the principal difficulties encounteredin the past has been that of leakage of the hydraulic uid. Anotherproblem that has been encountered is the liability of such devices tbreakage through improper handling. It has also been found generallynecessary in such devices to employ some form of external adjustingmeans which is subject to tampering and leakage and, altogether, thedisadvantages of such mechanisms have largely tended to. outweigh theadvantages thereof in the minds of most purchasers.

With the yadvent ofthe tremendous demand for a relatively simple andinexpensive automatic door closer which has accompanied the increaseduse of residential storm doors, the art has turned away from hydraulicor hydromechanical devices in favor of the less expensive pneumaticmechanisms of this character. Even so, however, such pneumaticmechanisms still generally require the use of some form of external`adjusting device and, although ordinarily somewhat less expensive thanthe hydro-mechanical devices, are generally less eicient in operation.

Accordingly, it -is a principal object of the present invention toprovide an automatic door closer of thehydromechanical type which isentirely self contained without any external adjusting means andwhich-may be readily and inexpensively manufactured to meet theinstallation and use requirements in residential dwellings.

Another object of the invention isto provide an automatichydro-mechanical door closer of thev type described employing novelclosure and packing elements so arranged as to substantially eliminatethe leakage-of hydraulic fluid generally found in such devices.

A further object of the-invention is to provide an automatic door closerof the type described utilizing a piston and cylinder arrangementinwhich `the piston assembly is capable of movement independent of its`associated piston p 2,949,625 Patented Aug. V23, 1960 iice rodparticularly during the power or door closing function.

An additional object of the invention is to provide a door closer of thetype described including a self contained yand automatically actingbypass arrangement to permit a forcedl rapid closing of the door withoutbreakage of the closer.V f

Yet another object of the invention is to provide a door closer of thetype described in which, by suitable manipulation, the door may be heldopen for a short time delay after which the automatic closing actionwill be resumed.

A still further object of the invention is to provide-a novel method andapparatus for assembling and refilling a hydraulic door closer of thetype described.:

Another object of the invention is to provide a novel stop pinarrangement for use in. a door closer of thetype described.

Another object of the invention -is to provide a hydro: mechanical door`closer employing a novel orifice arrangement in such manner as to effectaV relatively rapid and unobstructed movement of the door nearthe end ofthe closing cycle.

Yet another object of the invention is to provide a novel structure andmethod of mounting an automatic door closer in operating position insuch manner as to maintain aV residual door closingY force of uniformpredetermined amount.

The foregoing together with other andfurther. objects and advantagesofthe invention will become more readily apparent to one skilled intheart from a consideration of the following detailed description takenin conjunction with the accompanying figures of drawing. in which:

Figure 1' is a longitudinal cross-sectional view through a preferredform of door closer vin accordance with the present invention, showingthe same in mounted position upon ya door with the various parts in thepositions which they would normally occupy 'atrest or.with/ the doorclosed; y v

Figure 2 is av fragmentary, longitudinal, cross-sectional view similarto 'Figure l. but illustrating the position which certain ofthe partsoccupy during a door opening movement;

Figure 3 is Ia. fragmentary view similar to Figure 1 but showing therelative positions of certain of the parts during a normal door closingmovement; 'f

Figure 4 is a fragmentary view similar to. Figure 1 but illustrating therelative positions of certain of the parts dur-ing a door closing.movement inwhich a forced closing action has caused `automatic'operationof the bypass or. safety featureof the device;

Figure 5 is a fragmentary view similar to Figure 1 but showing therelative positions of certain of the parts when, during a door closingoperation, the door has been deliberately moved in such manner ase to'provide for holding the door open temporarily and for resumption 'ofautomatic door closing after a predetermined time delay;

Figure 6 is a longitudinal` cross-sectionalfview through the floatingpiston assembly in accordance with` the present invention buttoa-somewhat larger scale than shown in Figures` 1 throughS;

Figure 7 is a top plan view-of theI` piston assembly as shown -n Figure6 but with the cylinder shownin crosssection;

Figure 8 is a transverse cross-sectional view taken substantially alongthe line 8--8inr Figure 6;`

Figure 9 is a fragmentary, longitudinal, cross'dsectional view, to asomewhat enlarged scale, illustrating the-end closure and gland packingVat-the rod `end of the cylinder of Figure 1;

seals of Figure 9;

`Figures'lZ, 13, 14'an-d 4V15 arevfragmentary, `longitudinal,cross-sectionalviews, to a somewhat Venlarged scale,

illustrating the upper half only of the pistonl andl cylinderarrangement of Figure l land showing'rin'sequence, -the ,relationshipbetween the gas-liquid level at opposite sides of the fioating pistonassembly as the device goes through Ifracasan anoperating cycle', as aresult of which a relatively rapid f the end of the closingimovem'entj YFigure 16 is a longitudinal cross-sectional View of the right hand endof a piston` and cylinder arrangement as ,and unobstructedclosin/g'force isv applied'to the door near 'd shown in Figure 1 butillustrating a modified `form of the l n invention; e

'Figure 17 is a longitudinal cross-sectional view of the modified formof the device as shown in Figure 16 but illustrating the relativelpositions of the parts during an emergency or bypass operation; i

V vlFigures 118, 19 and '20 are longitudinal views in partialcross-section ofthe improved door closer as illustrated in Figure'l 'butillustrating, in sequence, the relative positions of the parts duringthe original assembly or Ire-filling operation; and

lustrating, in sequence, the method of mountingl the door closer upon a`door,'Figu`re 21 being generally in front elevation, and Figures 22, 23and 24 being top' plan views Aof the assembled device. y Referring nowin somewhat greater detail to thevarious figures of the drawing and' inparticular to Figure 1 thereof, the :improved door closer in accordancewith the present invention is seen to comprise al generally elongated,hollow cylinder 30 having its outer ends flared 'outwardly as indicatedby reference numerals 32 and 34. The rod end of the cylinder 30, or theleft end as viewed inFigure 1, `is'provid'ed with a suitable closure inthe form of acap :36having a central aperture 38 therein the door jambin -any convenient manner as by means of screws 66 and provided with aclevis or yoke 68 within which is pivotally mounted the flattened end ofa piston rod 70 which projects from the left hand end of the cylinderthrough the aperture 38 in the cap 36 and the wiper assembly 44. Theflattened end of the piston rod 70 is designated by referencepumeral 72and is provided with a pair of spacedapertures 74-76 for a reason whichwill hereinafter-be more fully explained. As shown in Figure 1,.,theflattened end 72 o f the piston rod 70 is held within'fthe clevis'orV'yoke 68 of the bracket 64 by means of a pivot pin 78 which passesthrough the single pair' of .apertures provided in-the opposite faces ofthe clevis 68 andthrough the, inner-aperture 76 in the flattened rod end72. i

As perhaps best illustrated in Figures 1, 6 and 7, the inner end of thepiston rod 70 which lies within the cylinder 30 is provided with afloating piston-assembly designated generally by reference numeraly 80,lThe piston assembly 80 is freely slidable axially along the piston rod70 within the cylinderl 30 between limit positions which may be definedas the left hand closure cap 36 and a stop pin 82 at the'right'ha'ndendof thepiston rod 70. As

y i* shown in Figure 7, the stoppin 82'is inserted into an aperture :84which extends transverselythrough the piston rod 70 and vwhich is uofa"dia metr somewhat larger than the diameter of the pin 82. However,lthe pin 82 is initially bent transversely inl such manner that it mustbe forced Figures 21 through 24 are largely schematic views ilwhile theright end of the cylinder 30 is closed by means of a solid cap 40, itbeing noted in both instances that the peripheral edges of the caps 36and 40 are crimped or otherwise suitably formed around the oppositeflared cylinder ends 32-34 in such manner as to be firmly held in placethereon. r The rod end 'of the cylinder '30 includes a packingassembly'which will hereinafter be more fully described and which isseen to comprise a composite annular washer 42 which liespartiallywithin land partially around theared cylinder end 32 and -a wiperassembly designated generally by reference numeral 44 comprising aplurality of composite annular washers, in the present case three innumber, thev outermost of which -lies within the aperture in the washer42, with an appreciable clearance, and abuts against the inner face ofthe closure or cap 36 around the aperture 38 therein. The right end ofthe cylinder 30 is provided with a disc shaped gasket lseal 46 which isheld in'place partially Within and partially around the flared end 34 bymeans of the cap 40.

As shown in Figure l, and perhaps even more clearly in Figures 21through 24, the cylinder 30 is adapted to be secured to a door 48 bymeans of a hingedbracket of any suitable design designated 'generally byreference numeral S0. The bracket 50 is seen -to comprise an arm 52which into the aperture 84 and', whennin theposition as illustratedinFigure 7, will be firmly held in place by resilient locking engagementwithin the aperture in a substantially 4centered position-therein.'

Referring particularly to Figure 6, the floating piston l,assembly 80comprises a thimble 86 having an internal diameter slightly larger thanthe outside vdiameter of the piston rod 70 and provided with outwardlyturned anges at its opposite ends. Mounted in lfixed position on thethimble 86 'are two axially spaced discs 88 and 90 lying at the oppositeends ofv the thimble adjacent the anges fon the latter and both havingloutside diameters appreciably smaller than the internal diameter of thehollow cylinder 30 Within which they`lie. Between the fixed discs 88 and90 there is provided a center disc 92 which is preferably formed of asuitable resilient material'such as rubber and which is movable axiallyof the thimble 86 between the fixed discs 88 and 90. l'The center disc92 is generally in the form of a' washer having its inside diameterappreeiabl'y'larger than the outside diameter of the thimble 86'andhaving its'o'utside' diameter in slidable 'sealing engagement withthe irinerfwall of the hollow cylinder 30.`

Still referring to Figuref 6, it will be noted that the internaldiameter of'the'mvable center disc 92 is sufficiently larger than theoutside diameter of the thimble 86 and the spacers 94 thereon to providea'relatively large aperture or oriiice 96 therebetween. The fixed disc88 at the right hand side ofthe floating pistonassembly 80 is providedwith a plurality ofv apertures or yorifices 98 so arranged as to lie insubstantial registry with the annual space between the inside diameterof the center disc-and the outside diameter of the spacers 94 yon thethimble constituting the orifice 96. It may also be observed atthis-point that when v thecenter disc 92 occupies any position spacedfrom the may be fastened to the door 48` in any convenient manner as bymeans of a screw 54 and an arm 56 suitably secured is adapted to be lefthand fixed disc '90,- there is provided a relatively unimpeded path offluid? fiow from the left hand end of the cylinder around theperiphery-of the fixed disc and through the orifices 96 and 98 into the righthand portion of .the cylinder 30. On the otherhand, when the center disc92 occupies itsextreme left hand position in abutting engagement withthe fixed disc 90,- the orice 96 will be 'closed against the facelof thedisc 9K0-so that the only path o f fluid ow from one -side 'of thepiston assembly 80 to the. other will be through theorifice, designatedby reference numeral 100,"- which constituted by .the annular Spacebetween theY inside diameter of the thimble 86 and the outside diameterof the piston `rod 70.

The operation of the floating piston assembly `80 will be hereinaftermore fully described but, as a general proposition, it may be statedthat the principal function of the floating piston assembly 80 is tocontrol the rate of transfer of uid from one side thereof to the otherthereby providing, in addition to the emergency bypass and time delayfunctions, for a relatively easy door opening movement and acorrespondingly slowed door closing action. 'I'he actual force toaccomplish a door closing operation is provided by the stored energy ofa helical compression spring 102. As shown in Figures l and 6, thespring 102 surrounds the piston rod 70 within the cylinder 30 and bearsat its right hand end against the fixed disc 90 o-f the iloating pistonassembly and at its left hand end against another disc or follower 104.Both the disc 90 and the follower 104 are cupped inwardly or otherwisesuitably shaped to receive the opposite ends of the spring 102 and, aswill be noted particularly in Figures l and 2, the follower 104 isformed with a guide bearing 106 surrounding the piston rod 70 and havinga rounded nose 108 bearing against the wiper assembly 44 and, throughthe latter, against the closure cap 36. `In actual practice it will beunderstood that during the initial assembly operation the compressionspring 102 is pre-loaded slightly so thatit will, at all times,yieldingly urge the piston assembly 80 and, through engagement of thelatter with the stop pin 82, the piston rod 70 inwardly or to the rightas shown throughout the various figures of the drawing.

yIn the modied form of the device as illustratedin Figures 16 and 17, anadditional coil spring 110 surrounds the piston rod 70 adjacent theright hand end of the latter and preferably lies within the primarycompression spring 102. The compression spring 110 bears at its righthand end against the iixed disc 90 and at its left hand end against acup shaped disc 112 which surrounds the piston rod 70 and bears againsta limiting means in the form of a stop pin 114. The operation of thismodified form of the device will likewise be hereinafter more fullydescribed.

As mentioned above, the principal function of the floating pistonassembly 80 is to control -the rate of flow of uid from one side thereofto the other and in order to provide for different rates of uid owduring opening and closing movements, the center disc 92 of the oatingpiston assembly operates somewhat in the manner of a valve byalternately `opening and closing the passageway or oriice 96 as the disc92 moves away from or towards the fixed disc `90. At such time as thecenter disc 92 lies against the face of the fixed disc 90, the only pathof fluid flow past the oating piston assembly is through the orifice 100formed between the inside diameter of the thimble 86 and the outsidediameter of the piston rod 70. In order to provide the orifice 100 withaccurately controllable dimensions, the piston rod 70 is machined orotherwise suitably formed in such manner as to provide a flat 116 -asparticularly illustrated in Figures 6, 7 and 8. In order to provide theemergency bypass feature of the floating piston assembly, as will behereinafter more fully described, the piston rod 70 is still further cutaway along a portion of its length adjacent the flat 116 to provide asecond ilat 118 of greater depth. The piston rod 70 to the left of theflat 118, as shown in Figure l, is of uniform circular cross-sectionuntil it reaches the attened end portion 72.

Referring now particularly to Figures 1, 2, 9 10 and l1 of the drawings,it will be noted that both the annular washer 42 and the disc shapedgasket seal 46 are yformed as composite members preferably comprisingtwo thin sheets of synthetic rubber or the like securely bonded to theopposite faces of a relatively stil plastic member. This plastic mayconveniently be of the phenolic thermoplastic type. As shown in Figure9, this laminated construction of seal 46 comprises the outer syntheticrubber layer 120, inner synthetic 4vrubberlayer 122, and the relaatively rigid or stilf plastic member 124 lying therebetween. It. is tobe particularly noted'in Figure 9 that the outer rubber layer is of a'larger diameter than both the inner element 122 and` the spacer 124.AThe gasket 46 at the right hand end ofthe cylinder 30 is similarlyconstructed except that it is not provided with Ia central aperture asin the case ofthe washer 42. In each'case, however, the packing assemblylies partially within and partially around the tlared end. of thecylinder in such manner that, when the closure cap 36 or 401A is'crimpedaround its associated' cylinder end, the inner element 122 forms a sealwithin the il-ared cylinder end while the projecting lip of the outerelement'120 is rmly held between the closure cap andthe end of thecylinder wall.

As inthe case of the gasket seal 46 land the annular washer 42, thewiper assembly 44` which comprises a plurality of composite, laminatedelements, utilizes similar principles to seal around the piston rod 70'.Asshown in Figure 9, the wiper assembly 44.com`prises three suchelements, each of which includes a pair of synthetic rubber, or thelike, members bonded zto opposite sides of a relatively rigid or stiifplastic meinberof similar composition to that used in seals 42'and'46.'In the case of the washers comprising the wiper'assembly 44, however,the outside diameter of all ofthe synthetic rubber and plastic elementsis the same whereas the inside diameter of Ione of the synthetic rubberelements of` each laminate is of smaller dimensions than theainsidediameters of its associated synthetic rubber and plastic elements. Thus,although each of the laminates 42.and 441is formed by the use ofsuitable dies in a punch press operation working upon laminatedl sheetmaterial, in the one case the extra sealing lip is provided' onthe.outer diameter, that is in the case of the element 42where'as in thecase yof the elements comprising the assemblyl y44, the sealing lip isprovided at the inner diameter in order to` achieve a proper wipingaction on the rodV 70. i

In connectionY with the wiper assembly 44, and contraryto the commonlyaccepted theory of operation, I have discoveredithatthe principalfunction of the wiper assembly 44 is to prevent the entrance of air intothe cylinder 30. In other words, as the piston rod 70 is withdrawn fromthe cylinder 30,the total available volume or empty space within thecylinderbecomesr somewhat greater so that a partial vacuum is'created.If air is allowed to enter the cylinder at' this time,then when thepiston rod '70' i's reinserted into the cylinder 30, that is, as theempty volume of the cylinder 30 is reduced', the lluid withinthecylinder -tends to be compressed and it is the resultant building up ofpressure within the iiuid which has, in the past, been a principalcauseof leakage. Accordingly, in accordance with the present invention theindividual washers of the wiperassembly -44 are so arranged aboutthepiston rod 70 as'to provide their maximum wiping elTectiveness-as therod is being withdrawn from the cylinder.

It will also 'be particularly noted in Figure 9 that there is provided asubstantial clearance between the outermost washer of the wiper assembly44 and the internal diameter of the annular washer 42. Since theinnermost washer yof the wiper assembly 44 bears against the roundednose 108 of the thimble or sleeve 106 against which the 4force of thecompression spring 102 is directed, as the compression of the spring 102is increased the pressure of the rounded nose 108 against theinner'washer is likewise increased thereby giving a proportionalincrease in the sealing action of the washer againstA the rod 70. 0n theother hand, contrary to the usual arrangement of a conventional glandpacking, there is nov rigid confining force surrounding the wiperassembly 44 so that whatever vswelling may take place due to fluidabsorption, or the like, will not tend toincrease the pressureL ofthewiper elements against the rod `70.

Operation Before proceeding with a complete description of the operationof the device, reference will be made to the improved method andapparatus for assembling the device as illustrated in Figures .18, 19and 20, and to my improved method of mounting the same in operativeposition upon a door as illustrated in Figures 21 through 24. yReferringnow .speciiically to Figure ,18, the rst step in assembling the Ydeviceis to place the gasket seal 46 in position 'partially .Within andpartially around the flared cylinder end 34and securely'hold the same 'mseal- .ing position .byv means of crimping the closure cap 40therearound. It will be understood that the closure cap 40 haspreviously been riveted to themounting bracket 50 so that the bottom endof the device as shown in Figure 18 is completely assembled by thissimple operation. The floating piston assembly and piston rod are thenassembled by forcing the stop pin 82 into position and sliding thecomplete iioating piston assembly over the lflattened rod end 72.l Thecompression spring 102 is next slid over the attened rod end 72 and thefollower 104 and wiper assembly l44 likewise slid over the attened rodend 72. `At this point an assembly tool in the form of a simple cylinder126 is slid over the flattened rod end 72 and', with the rod andfloat-ing piston assembly in a suitable jig, or the like, the cylinder126 is forced inwardly against the wiper assembly 44 and against theforce of the compression spring 102 and held in place by means of aremovable stop pin 128 which is `temporarily inserted through one of theholes provided in the attened rod end `72 At this point the rod andiioating piston assembly may be inserted downwardly into the cylinder 30and the latter may be illed to the desired point in any convenientmanner as indicated by the filling nozzle 130. It will be understoodthat the level of liquid within the cylinder 30 may be adjusted to givemost eicient operation and I have found that while various types ofhydraulic fluid maybe employed, a .mixture of water and the well-knownanti-'freeze sold under the trade name Prestone (substantially ethyleneglycol) provides eilicient all weather operation.

The rod end of the cylinder 30 is now ready to be closed and in order toaccomplish this, the composite annular washer 42 is slid over and aroundthe cylindrical assembly tool`126 followed by the closure cap 36 whichis then crimped around the ared end 32 of theV cylinder 30 therebysecurely sealing the latter. This portion of the assembly is illustratedintl-"figure 19 and upon completion of the above enumerated steps, thepin 128 may be withdrawn thereby permitting the assembly tool 126 to beslid upwardly by the'force of the compression spring 102 thereby forcingthe wiper assembly 44 into the annular space within the washer 42 andinto firm sealing engagement with the closure cap 36.

It will be understood that during the entire assembly operation thus fardescribed, substantially no pressure has been placed upon the uid withinthe cylinder 30. This is contrary to the usual practice in which theclosure, containing a packing gland or the like is slid over the rod endand screwed onto the cylinderthereby producing a residual pressurewithin the contained Huid. By eliminating such residual pressure thereIis no tendency on the part of the assembled device to leak followingthe inal 4assemlby operation as illustrated in Figure 20. Additionally,and of considerable importance, if at any time it should becomenecessary or desirable to add fluid to the device after iinal assembly,it is a relatively simple matter to reapply the assembly tool 126 tocompress the spring 102 and thereby provide an aperture Yinto whichadidtional tluid may be poured following which the-tool 126 may -beremoved in the manner previously described. In this-way it isunnecessary to re'- move the closure cap 36 for the purpose of addingfluid at any time during the life of the device.

After the device has been assembled in the manner just described, lit isnow ready for installation upon a door in a manner as illustratedschematically in Figures 21 through 24. Referring particularly to Figure21, the door closer is shown in completely installed condition with thebracket 64 secured to the door jamb 62 by means of the screw 66 land thefitting S0 attached to a portion of the frame of the door 48 by means ofthe screw 54. It will be particularly noted in Figure 21 that when thedoor closer is properly installed, the screw or bolt 78 which attachesthe piston rod 70 to the clevis or yoke 68 of the bracket 64 extendsthrough the hole 76 which is nearer to the cylinder 30 rather thanthrough the more remote hole 74. For convenience in the followingdescription the hole or aperture 76 will be referred to as the innerhole and the hole or aperture 714 will be referred to as the outer hole.

Referring now to Figure 22, the initial step in the installation of the`door closer is shown in full lines. After the bracket 64 has beenmounted on the door jamb 62, the bolt 78 is inserted through the yoke 68and through the outer hole 74 in the attened end 72 of the piston rod70. With the door 48 firmly closed, the bracket 50 is next attached tothe door frame by means of the screw 54.` Following this, the door 48 ispartially opened thereby exerting a force on the spring 102, compressingthe same partially, and causing the rod to project somewhat farther fromthe cylinder 30. At this point the manual locking `ring 132 is slid tothe right along the piston rod 70 to bear against the closure cap 36 asshown in dotted lines in Figure 22, thereby locking the cylinder rod 70in partially extended position in a manner well known to those skilledin the art.

After the piston rod 70 has been locked in partially extended position,pressure may be removed from the door 48 and the bolt 78 removed fromthe clevis or yoke 68 and the outer hole 74. Following removal of thebolt 78, the door 48 may be closed slightly thereby causing the pistonrod 70 to move slightly to the left relative to the bracket 64 so thatthe bolt 78 may be reinserted through the yoke 68 and, `this time,through the inner hole 76. Following this operation, the door 48 may bepushed out slightly thus relieving the force upon the manu-al lockingring 132 and permitting the latter to be slid to the left whereupon thedoor may be permittedl to close under the force of the compressionspring 102. Since the door attaching bracket 50 is not moved during thisinitial assembly oper-ation, the `linal position of the piston rod 70,as shown in Figure 24 and also in Figure 2l, is slightly extendedthereby placing an laccurately predetermined amount of residualcompression upon the spring 102 and thereby exerting a continuous slightforce tending to hold` the door 48 firmly in closed position. It is tobe understood that the spring 102 has been initially pre-loaded by theoriginal assembly operation and that the additional loading accomplishedthrough utilization of the inner and outer holes in the rod end in themanner just described serves merely as a slight additional loading tokeep the rod 70 a small distance away from the right hand closure cap 40when the door is fully closed. `Of considerable importance also is thefact that since the spacing of the holes 74 and,76 is accuratelypredetermined to give the desired residual compression in the spring102, the likelihood of faulty installation is minimized. The operationof the door closer is illustrated in Figures 1 through 5 whichparticularly show the relative positions of the cylinder, iioatingpiston assembly, and piston rod at various stages in the operatingcycle. As illustrated in Figure 1, the door closer is assumed to befully assembled and installed between a door and door jamb in the'manner previously described. With the door closed,-the variou-srpartsof the door closer will occupyl approximately the positions illustrated'in Figure 1 wherein 'it' willbe noted that the piston rod 70 is spacedaway from the right hand closure cap 40 a distance approximately equalto the dist-ance between the inner and outer holes 76 and 74. Thus, theresilient pre-loaded compression force` of the spring 102 is appliedthrough the stop pin 82'to the piston rod 70 and is continuouslyeffective to cause the door to remain in closed position. As shown inFigure 1, the movable center disc 92 of the floating piston assembly 80will probably occupy some intermediate position between the fixed discs88 and 90 so that the level of the liquid (which occupies the majorportion of the space within the cylinder 30) is substantially even atopposite sides of the floating piston assembly.

With the door closer in the door closed or rest position of Figure 1, ifthe door is moved to start a door opening operation the parts of thedoor closer will assume the relative positions as shown in Figure 2. Asillustrated in this View, the piston rodv 70 is moving to the left and,by means yof Ithe engagement of the stop pin 82 with the thimble 86, iscarrying with it the floating pis-ton assembly 80 thereby tending tofurther compress the spring 102. During this movement of the floatingpiston assembly 80, the movable center disc 92 will be moved to theright against the face of the fixed disc 88- by reason of the slightfrictional engagement of the outer periphery of the disc 92 with theinner wall o-f the cylinder and, primarily, by the pressure of the fluidat the left hand side of the floating piston assembly. With the movablecenter disc 92 in the position as illustrated in Figure 2, it will benoted that the annular orifice 96 is substantially in registry with theorifices 98 so that fluid at the left hand side of the floating pistonassembly is afforded a relatively unobstructed path of flow around theoutside ofthe fixed disc 90, through the orifice 96, and through theorifices 98 into the space within the cylinder 30 at the right hand sideof the floating piston assembly 80; At the same time, fluid at the lefthand side of the floating piston assembly may also flow to the righthand side thereof through the orifice 100 which is provided between theinside diameter of the thimble 86 and the flat 116; on the piston rod70. Such flow of fluid through the orifice 100 is, however, much smallerthan the unobstructed flow around the disc 90 `and through the orifices96 and 98 and, during this phase of the operation of the door closer, isof relatively minor significance.

After the door has been opened to the desired extent, normally theperson using the door will simply release the same thus permitting thedoor closer to return the door to closed position. If the door isIoperated in this manner, the relative position of the parts of the doorcloser after the door has been released is illustrated in Figure 3wherein, as shown by the arrow, the piston rod 70 is moving to the rightor into the cylinder 30. Since there is no external force being appliedto the door at this time, the only force tending to close the door isderived from the stored energy of the compression spring 102 which bearsagainst the fixed disc 90 and thimble 86 thereby transmitting such forcethrough the stop pin 82 ito the piston rod 70. As the door closes underthe force of the compression spring` 102 as shown in Figure 3, thefluid'at the right hand side of the floating piston assembly {l-'must now pass back tothe left hand side of the floating pistonpassembly.However, both the slight frictional'engagement of the movable centerdisc 92 with the inner wall-'of the cylinder30 and the pressure of thefluid within thel cylinder30 -atthe right hand side of the floatingpiston assembly will now cause the moyable disc 92 to move tothe leftrelative to the fixed discs 88 and 90 so that it will lie flat againstthe face of the fixed disc 90. In this position of the movable centerdisc 92, the annular orifice 96 will be substantially obturated therebyclosing the path of fluid flow through the floating piston assembly asillustrated'in Figure 2f Since the path of fluid flow through the.orifices-98 `and-96 and around the outer periphery of thefxedfdisc 90 isnow closed, the fluid 'at the right hand side of thevfloating'piston'rassembly mustnow pass to the left vhand side ofthefloating piston assembly through the relatively small orifice 100.Since, as previously mentioned, the orificer 100 can be carefullycalibrated by controlling the dimensions of the flat 116 and the size ofthe inner diameter of the thimble 86, it will be apparent that if thedoor is allowed to return to closed position solely under the impetus ofthe compression spring 102 in the manner illustrated in Figure 3, suchdoor closing movement will be at a relatively slow rate under thecontrol of fluid flow through the relatively small orifice 100.

Although the door cl-oser is intended to operate normally in the-mannerillustrated in Figure 3, it occasionally happens, particularly when thedoor is used by children, that an external force will be applied to thedoor over and above that applied by the compression spring 102 tendingto force or slam the door closed. When this occurs, the parts of thedoor closer assume the positions as illustrated n Figure 4 wherein theautomatic bypass becomes effective thereby preventing damage to thecloser. As shown in Figure 4, if, during a normal closing movement ofthe door is previously described in connection with Figure 3, anexternal force is applied tending to force the door closed, the pressureof the fluid within the cylinder 30 at the right hand side lof thefloating piston assembly will increase more rapidly than it may bedissipated by flow through the relatively restricted orifice As aresult, the entire floating piston assembly 80 will be forced to theleft relative to the piston rod 70 and into a position such that thethimble 86 will now surround that portion of the piston rod 70 in theregion of the flat 118`. Since the flat 118 is considerably deeper thanthe flat 116, the effect is toI provide a relatively much larger orice134 thereby relieving the excess pressure on the fluid at the right handside of the floating piston assembly 'and permitting the fluid to passfreely to the left hand side of the floating piston assembly so long asthe external force is applied to the door.

If the external force applied to the door tending to force the sameclosed is no greater than a predetermined amount which can be absorbedby movement of the floating piston assembly in the manner illustrated inFigure 4 to open up the larger orifice 134, the floating piston assemblywill move back to the position as illustrated in Figure 3 as soon as theexternal force is removed. However, since the entire floating pistonIassembly 80 may move in an unobstructed manner between limits definedby the `stop pin 82 and the closure cap 36, if a force tending to closethe door is' applied externally in an amount greater than that which canbe absorbed by movement of the floating piston assembly to the positionof Figure 4, the piston rod 70'will simply continue to move relative tothe floatngpiston assembly 80 into some position such as thatillustrated in Figure 5. It is to be clearly understood that suchcontinued movement of the piston rod 70 relative to the floating pistonassembly 80 can in no way damage the-door closer since, las previouslypointed out, the entire floating piston assembly is free to moverelative to the piston rod 70.

Still referringl to Figure 5, and although the position of the parts as'illustrated in this view has been described as representing an extremecondition beyond that which can be accommodated by the emergency bypassposition of Figure 4, it may occasionally be desirable to operate thedoor deliberately in such manner as to force the floating pistonassembly into a position such as illustrated in Figure 5. For example,if the person using the door should have an -armful of bundles, or thelike, or for any other reason lshould wish to'hold the door open for abrief time delay interval, it is only necessary to apply a door closingforce of a magnitude sufllcient to move the floating piston assemblyinto the position of Figure 5. In this position the flow of fluid fromthe right hand side of the floating pistonassembly to the left hand sidethereof is still further restrited tothe actual 'clearanceprovidedbetween the inside diameter of the thirnblelv and the outside diameterof the piston rod 70. The orifice thus provided is extremely small sincethere is no flat'on the piston rod at this point and, as -a result, theclosing force of the spring 102 will be effectively blocked by thepressure of the tiuid at the right hand side ofthe floating pistonassembly until such time as a sufficient volume of uid has leakedthrough this very small orifice |around the piston rod to permit theoating pistonasisembly 80-to move back or to the right in Figure to aposition over the flat 118. Since the orice between the inside diameterof .the thirnble 86 and the outside diameter of the piston rod 70 is soextremelysrnall, the net effect of placing the floating piston assemblyinto the position of Figure 5- is to introduce a time delay in thenormal door closing action of the spring 102 during which intervalthe-user may pass through the door and following which the spring 102will again become effective to close the door in a normal manner. A

In the modiiied form of the device, as illustrated in Figures 16 and 17of thedrawings, the'construction of the parts is substantially identicalto that already described except for the addition of the second coilspring `110 which extends between the fixed disc 90 and the follower 112which in turn is held in place against the stop pin 114. In Figure 16the parts are shown in the positions which they would normally occupywith the door closed asin Figure 1. However, when an external 4force isapplied tending to close the door in a manner as previously described inconnection with the operation illustrated in Figures 4 and 5, the oatingpiston assembly 80 of Figure 16 will move to the position as illustratedin Figure 17. In this way, an enlarged orice 134 is again uncovered asin Figure 4, thereby preventing damage to the closer mechanism. However,with the modified form of the device, as illustrated in Figures 16 and17, it is possible by proper selection of the extra compression spring110 to more accurately predetermine the amount of excess force whichmust be applied to the door in order to bring about the emergency bypassactuation of the floating piston assembly. Thus, by merely changing thestrength of the auxiliary compression spring 110 and without anysubstantial modification of the remainder of the door closer assembly,it is possible to adapt the modified form of the device, -as shown inFig ures 16 and 17, to a wide variety of different installationconditions.

When the door closer is installed in the manner illustrated in Figures21 through 24, it will be recalled that the pre-loaded compressive forceof the coil spring 102 is continuously applied to the door 48 in suchmanner as to tend to hold the latter firmly in closed position. Despitethis advantage, however, it will still be apparent that the storedenergy of the 'compression spring 102 is at its lowest value near thevery end 'of a door closing operation. Furthermore, it is at this exactpoint that a slight additional push is normally required in order toirmly engage the door latch with its keeper. In accordance with thepresent invention I have provided for such an action as illustrated inFigures 12 through 15.

Referring specifically to Figures l2 through 15, it is to be noted firstof all that the door closer has been shortened considerably by breakingthe views and, in each case, the figure shows only the upper half of thedoor closer above the center line of the piston rod 70 in order toprovide a sufficiently enlarged scale to illustrate the action whichtakes place in operation. As shown in Figure 12, the door closer isassumed to be fully installed, in the manner previously described, upona door and its associated jamb and the door is assumed to be closed orin the rest position. At this time, the movable center disc 92 isfurther assumed to occupy a position somewhere intermediate the fixeddiscs 88 and 90 and, although there is a relatively unobstructed pathJfor uid how past the oating piston assembly 80, since theparts are atrest there is noflow taking place. It is to be particularly noted inFigure 12 that, since the cylinder 30 is initially filled with liquid toa point which almostoccupies its entire volume, there is a relativelysmall residual volume of air which remains in the cylinder 30. This air,as shown in Figure 12, lies along the top of the cylinder 30 which ismounted in horizontal position Vand the level of liquid at the righthand side of the floating piston assembly is substantially the same asthe liquid level at the left hand side thereof.

When a door opening operation is begun, the movable disc 92, aspreviously described, will move to the right relative to the` fixeddiscs 88 and 90 and will lie against theface of the fixed disc 88thereby opening upa relatively unobstructed path of iuid flow around theouter periphery of the fixed disc 90 and through the orices 96 and 98. Apath of fluid flow through the inner orifice 100 is also available butis of relatively much smaller dimensions than that previously mentioned.Accordingly, as the initial door opening movement takes place, andparticularly in view of the ease of ow ofthe air as compared to theliquid, there is a tendency for substantially all of the air lyingadjacent the top of the cylinder 30 at the left hand side of theoatingrpiston assembly to ow over the fixed disc 90 and thencedownwardly through the orifices 96 Iand 98 before any ap'- preciablequantity of the liquid at the left hand side lof the floating pistonassembly begins to move to the opposite side of the latter. During suchinitial door opening movement, therefore, substantially the total volumeof air within the cylinder 30 will move to the right hand side of thefloating piston assembly so that, as illustrated in Figure 13, therelative proportion of lair to liquid at the right hand side of thefloating piston assembly tends to increase.

When the door is fully opened, the floating piston' assembly will occupyits maximum position to the left and, at that time, the relative volumeof air to liquid at the right hand side of the floating piston assemblywill again be reduced so that the liquid level will approach theprevious position which it occupied with the parts at rest. However, asthe door begins to close, as shown in Figure 14, the movable center disc92 immediately moves against the face of the fixed disc 90 therebyclosing the path of fluid flow through the orifice 96. Since, at thistime, the level of the liquid at the right hand side of the o'atingpiston assembly lies above the only available path of fluid flow whichis through the centrally located orifice 100, the air tends to remain atthe right hand side of the floating piston assembly and, as the lattermoves to the right, the relative volume of air to liquid at the rig-hthand side of the floating piston assembly tends to increase as liquidmoves to the left hand side of the floating piston assembly through theorifice 100.

As the relative proportion lof air to liquid increases during movementof the floating piston assembly to the right in a door closingoperation, eventually the piston rod 70 and the floating piston assembly`80 will reach a position as shown in Figure l5 wherein sufficientliquid has passed through the orifice 100 so that the liquid level atthe right hand side of the floating piston assembly is low enough topermit air to likewise pass through the orifice 100. In view of theviscosity of the liquid and its inherent greater resistance to ow, atthis point the air at the right hand side of the floating pistonassembly will surge relatively freely through the orifice 100, and,since this position of the parts is predetermined in such manner as tooccur just prior to the final closing move ment of the door closer, itfollows that such final closing movement is relatively unirnpeded andprovides the necessary impetus to force the door latch into firmengagement with its associated keeper.

Although I have shown and described herein certain preferred embodimentsof apparatus solely for the pur pose of illustration, it will be obviousthat numerous modifcations, alterations and deviations will occur tothose Skilled in the art withoutrdeparting from the spirit or scope ofthe invention as set forth in the following claims. Having thusdescribed my invention what I claim as new and desire to secure byLetters Patent is as follows:

l. A door closer comprising a generally elongated, hollow cylinderhaving outwardly ared ends, closure caps crimped around the oppositeiiared cylinder ends, one of said caps having a central aperture thereinand the other of said caps having an external hinged bracket forattachment to a door, gasket seals held within each of Said flaredcylinder ends by its associated cap, a solid cylindrical piston rodextending into said hollow cylinder through said apertured cap having astop pin at its inner end and a bracket at its outer end for connectionto a door jamb, a piston freely slidable axially along said rod withinsaid hollow cylinder between said apertured cap and said stop pin, saidpiston comprising a tubular thimble having an internal diameter slightlylarger than said solid rod, axially spaced `discs xed at opposite endsof said thimble having outside diameters substantially smaller than theinternal diameter of said hollow cylinder, and a center disc ofresilient material movable axially of said thimble between said lxeddiscs having its inside diameter substantially larger than the outsidediameter of said thimble and its outside periphery in slidable sealingengagement with the inner Wall of said hollow cylinder, a compressionspring extending between said apertured cap and one of said xed discsurging said piston inwardly, the other of said xed discs having aplurality of apertures substantially in registry with the annular spacebetween the inside periphery of said center disc and the outsideperiphery of said thimble, and a plurality of adjacent ats extendingalong said rod, said Hats being of different widths, thereby to provideorifices of different areas between said rod and the inside periphery ofsaid thimble at diierent positions of said piston along said rod wherebyuid may pass from one side of the piston to the other, within saidcylinder, at variable rates governed by the areas of the respectiveorifices.

2. A door closer comprising a hollow cylinder, closure caps on theopposite cylinder ends, one of said caps having a central aperturetherein, gasket seals held within each of said cylinder ends by itsassociated cap, a solid cylindrical piston rod extending into saidhollow cylinder through said apertured cap having a stop pin at itsinner end, a piston freely slidable axially along said rod within saidhollow cylinder between said apertured cap and said stop pin, saidpiston comprising a tubular thimble having ari-internal diameterslightly larger than said solid rod, axially spaced discs fixed atopposite ends of said thimble .having outside diameters substantiallysmaller than the` internal `diameter of said hollow cylinder, and acenter disc ofl resilient material movable axially of said thimblebetween said fixed discs having its inside diameter substantially largerthan the outside diameter of said thimble-and its--outside periphery inslidable sealing engagement with` the inner wall of said hollowcylinder, a compression spring extending between said apertured cap andone of said fixed discs urging said piston inwardly, the other of saidiixed discs having a plurality of apertures substantially in registrywith the annular space between the inside periphery of said center discand the outside periphery of said thimble, and a plurality of adjacentilats extending along said rod, said flats being of diierent widths,thereby to provide orifices Iof different areas between said rod and theinside periphery of said thimble at dilerent positions of said pistonalong said rod whereby fluid may pass from one side of the piston to theother, within said cylinder, at variable rates governed by the areas ofthe respective oriiices.

3. A door closer comprising a hollow cylinder, closure caps on theopposite cylinder ends, one of said caps having a central aperturetherein, a piston rod extending into said hollow cylinder through saidapertured cap having a stop pin at its inner end, a piston freelyslidable axially along said'rod within said hollow cylinder between saidapertured cap and said stop pin, said piston comprising a tubularthimble having an internal diameter slightly larger. than said rod,axially spaced discs iixed at oppositel ends of said thimble havingoutside diameters substantially smaller than the internal diameter ofsaid hollow cylinder and a center disc of resilient material movableaxially of said thimble between said iixed discs having its insidediam-eter substantially larger than the outside diameter of said thimbleand its outside periphery in slidable sealing engagement with the innerwall of said hollow cylin-` der, a compression spring extending betweensaid apertured cap and one of said iixed discs urging said pistoninwardly, the other of said fixed discs having a plurality of aperturessubstantially in registry with the annular; space between the insideperiphery of said center disc and the outside periphery of said thimble,and a plurality of adjacent flats extending along said rod, said ilatsbeing of diierent widths, thereby to provide 'orifices of differentareas between said rod and the inside periphery of said thimble atdifferent positions of said piston along said rod whereby uid may passfrom one side of the piston to the other, within said cylinder, atvariable rates governed by the areas of the respective orices.

4. A door closer comprising a cylinder, a piston rod extending into saidcylinder having a stop pin at its inner end, a piston freely slidableaxially along said rod within said cylinder, said piston comprising atubular thimble having an internal diameter slightly larger than saidrod, axially spaced discs xed at opposite ends of said thimble havingoutside diameters substantially smaller than the internal diameter ofsaid cylinder, and a center disc of resilient material movable axiallyof said thimble between said xed `discs having its inside diametersubstantially. larger` than the outside periphery of said thimble andits outside diameter in slidable sealing engagement with the inner wallof said cylinder, spring means bearing against one of said fixed discsurging said piston against said stopA pin and into said cylinder, theother of said xed discs having a plurality of apertures substantially inregis-A try with the annular space between the inside periphery of saidcenter disc and the outside periphery of said thimble, and a pluralityof adjacent flats extending along. said rod, said flats being ofdiiferent widths, thereby to provide orilices of different areas betweensaid rod and the inside periphery of said thimble at different positionsof said piston along said rod whereby liuid may pass from one side ofthe piston to the other, within said cylinder, at variable ratesgoverned by the areas of the respective orifices..

5. A door closer comprising a closed cylinder substan-V tially lledwithhydraulic uid, a piston rod extending into said cylinder in pressuresealed relation therewith, a piston freely slidable axially along saidrod within said cylinder, stop means on said rod limiting relativevmovement of saidV piston in onel direction, and spring` meansyieldinglyurging said piston against said st-op means and into said cylinder, saidpiston comprising a tubular thimble having an internal diameter slightlylarger than said rod, axially spaced discs `fixed at opposite ends ofsaid thimble having outside diameters substantially smaller than theinternal diameter of said cylinder, and a center disc of resilientmaterial movable axially of said thimble between said iixed discs havingits inside diameter substantially larger than the outside diameter ofsaid thimble and its outside periphery in slidable sealing engagementwith the inner wall of said cylinder, lone of said lixed discs having aplurality of apertures substantially in registry with the annular spacebetween the inside periphery of said center ldisc and the outsideperiphery of said thimble.

6. A door closer comprising a cylinder adapted to be substantially lledwith hydraulic il'uid, a piston rod extending into said cylinder, meanslimiting movement of said piston in one direction relative to said rod,and means yieldingly urging said piston towards said limiting means,said piston comprising a tubular thimble having anv internal diameterslightly larger than said rod, axially spaced discs iixed at oppositeends of said thimble having outside diameters substantially smaller thanthe internal diameter of said cylinder, and a center disc movableaxially of said thinrble between said fixed discs having its insidediameter substantially larger than the outside diameter of said thimbleand itsoutside periphery in slidable sealing engagement with the innerwall of said cylinder, one of said iixed discs having a plurality ofapertures substantially in registry with the annular space between theinside periphery of said center disc and the outside periphery of saidthimble.

7. A door closer comprising a cylinder adapted to be substantiallyfilled with hydraulic uid, a piston rod extending into said cylinder, apiston slidable axially along said rod within said cylinder, meanslimiting movement of said piston in one direction relative to said rod,and means within said cylinder yieldingly urging said piston towardssaid limiting means, said piston comprising a member in slidable sealingengagement with the inner wall of said cylinder, said piston rod havinga plurality of reduced sections of different size along which the pistonmay travel thereby providing a variable orice between said piston androd permitting variable ow of fluid past said piston in accordance withthe position of said piston relative to said rod, and second orice meansin said piston operable to provide a path of ow of said uid past saidpiston during movement of the latter in one direction and to obturatesaid path of ilow of iluid past said piston during movement of thelatter in the opposite direction.

8. In a door closer having a cylinder adapted to be substantially iilledwith hydraulic fluid and a piston rod extending into said cylinder, apiston slidable axially along said rod within said cylinder andcomprising a member in slidable sealing engagement with the inner wallof said cylinder, said piston rod having a plurality of reduced sectionsof diierent size along which the piston may travel thereby providing avariable orice between said piston and rod permitting variable ilow offluid past said piston in accordance with the position of said piston'relative to said rod, and second orifice means in said piston operableto provide a path of iiow of said fluid past said piston during movementof the latter in one direction and to obturate said path of flow offluid past said piston during movement of the latter in the oppositedirection.

9. In a door closer having a cylinder adapted to contain fluid and apiston rod extending into said cylinder, a piston slidable axially alongsaid rod within said cylinder and comprising a member in slidablesealing engagement with the inner wall of said cylinder, said piston rodhaving a plurality of reduced sections of different size along which thepiston may travel thereby providing a' variable orifice between saidpiston and rod permitting variable flow of fluid past said piston duringmovement of the latter in both directions, and second vorifice means insaid piston operable to provide a relatively unrestricted path of ow ofsaid fluid past said piston during movement of the latter in onedirection and to obturate said path of flow of fluid past said pistonduring movement of the latter in the opposite direction.

10. A door closer comprising a cylinder adapted to be substantiallyyiilled with hydraulic luid, a piston rod extending into said cylinder,a piston slidable axially along said rod within said cylinder, meanslimiting movement of said piston in one direction relative to said rod,rst spring means biased between said cylinder and said piston andyieldingly urging the latter towards said limiting means, and secondspring means biased between said rod and said piston independentlyurging the latter towards said limiting means, said piston comprising amember in slidable sealing engagement ywith the inner wall of saidcylinder, said piston rod having a plurality of reduced sections ofdifferent size along which the piston may travel thereby providing avariable orifice between said piston and rod permitting variable ow ofiluid past said piston in accordance with the position of said pistonrelative to said rod, and second oritice means in said piston -operableto provide a path of ow of said uid past said piston during movement ofthe latter in one direction and to substantially obturate said path ofow of uid past said piston during 4movement of the latter in theopposite direction.

l1. In a door closer having a cylinder adapted to contain iluid and apiston rod extending into said cylinder,

a piston movable relative to said rod within said cylinder, meanslimiting movement of said piston in one direction relative to said rod,rst spring means biased between said cylinder and said piston andyieldingly urging the latter towards said limiting means, and secondspring means biased between said rod and said piston independentlyurging the latter towards said limiting means, said piston rod having aplurality of reduced sections of different size along which the pistonmay travel thereby providing a variable orifice between said piston androd permitting variable ow of uid past said piston inV accordance withthe position of said piston relative to said rod, and second oriiieemeans in said piston operable to provide a path of flow of said fluidpast said piston during movement of the latter in one'direction and tosubstantially obturate said path of flow of fluid past said pistonduring movement of the Vlatter in the opposite direction.

References Cited in the le of this patent UNITED STATES PATENTS

